This article should be a good start for answering some of these questions: How Does Smart Review Work?
We used to add all phrases from lessons automatically, so if you used the website at all before February 2022, then that’s likely a big part of the reason for the large backlog.
Now we’ve changed things and have started giving you manual control of which phrases you want to add at the end of each lesson (and from the other content). That way you only choose what’s most relevant to you and it helps reduce the backlog. But this only applies from mid-February on, as we didn’t want to clear anyone’s Smart Review out without permission of course.
Overall, I wouldn’t worry too much about the number. The more important thing is just doing your best to review on a regular basis. If you’re doing regular reviews, and being thoughtful about the phrases you’re adding, the numbers should naturally start to go down over time. They don’t budge much in the beginning because the intervals are still very short. But once you get each one right a few times, the intervals increase and it will be much longer until each one is added to a review again.
If it’s bothering you now, then I would recommend continuing to make more manual adjustments on the Manage Smart Review page (either Removing or marking as Mastered), or asking us to clear it out to start from scratch.
But otherwise, you’re right that it may take months. This is in line with the long-term nature of reviewing what you’re learning, but I do understand it’s frustrating to see that high number when you’ve done so much hard work!
We are (gradually) working on some changes that should give a lower emphasis to the number “due” going forward, but we still keep it around for now because some people do find it useful. And with the new changes, we are hoping Smart Review will become more manageable anyway. The starting backlog is just an unfortunate side effect of us not having the ‘manual add’ feature from the very beginning.
Let me know if you have any other questions or if I can help at all with the phrase management process!